The present invention relates to portable pumping devices capable of operating either as a suction pump or as a compressor. The invention is particularly applicable to the portable fluid pumping devices described in my prior U.S. Pat. No. 4,726,745, and is therefore described below with respect to this type of device.
My U.S. Pat. No. 4,726,745 discloses a portable pumping device particularly useful as a medical suction pump for drawing off waste fluids. The pumping device described in that patent is now in production, but one of its drawbacks is that it requires a rolling diaphragm between the piston and cylinder. Rolling diaphragms, however, degrade with time and deform under pressure to introduce "dead" piston travel which stretches the diaphragm without displacing air. Such pumps, therefore, require frequent replacement of the diaphragm.
In addition, pumps of this type are extremely noisy at the exhaust end when operating as a suction pump, and at the air-intake end when operated as a compressor. One source for such noise is the one-way umbrella valves commonly used in such pumps. Thus, the common umbrella valve construction includes a dome-shaped umbrella skirt integrally joined to the neck of a stem received within a mounting opening formed in a wall, which wall is also formed with the valve opening covered by the umbrella skirt. Such umbrella valves require high seating forces which generate a high pitch noise. In addition, such umbrella valves are difficult to produce by injection molding and require high precision in the mounting opening.